STATEN ISLAND, N.Y. -- Mayor Michael Bloomberg is urging families who were evacuated from their homes not to return until the city can be sure the building is structurally sound.

The mayor, in a news conference Wednesday afternoon, said the city's Zone A evacuation order will remain in effect until city inspectors can certify that buildings are safe.

He said inspectors will be going block-by-block into storm-ravaged neighborhoods in Zone A to inspect homes. Each building will be color-tagged, with a red tag meaning the structure is not safe to return to; a yellow tag meaning proceed with caution, and a green tag signifying the building is safe and structurally sound.

The city Buildings Department will be doing the majority of inspections, but the mayor said that independent contractors, engineers, and other personnel with a knowledge of construction can be self-certified to perform the inspections.